Asynchronous motors, with conical rotor and brake, where the rotor magnetic field generates, besides the rotation torque, a rotor axial movement, deblocking the brake, are well known. These motors have the disadvantage of a very complicated construction, are difficult to build from a technological viewpoint, and result in an abnormal use of the magnetic circuit and of the driving shaft displacement when connected or disconnected to the power line.
Asynchronous motors with braking, where the brake-deblocking electromagnetic force is obtained using the magnetic field created by the current flowing through the rotor short-circuiting ring, are also known. These motors have the disadvantage that the motive force that acts upon the brake deblocking armature diminishes significantly from the starting moment to the moment of reaching the operational speed, the final value of this force being very low and precluding the obtaining of sufficient braking torques.
There are also asynchronous motors with brakes where, in order to generate the brake-deblocking force, the stator inductive magnetic field is used, the stator being longer than the rotor, the respective supplementary portion being conically turned hollow, so that the brake-deblocking armature active zone enters the hollow and has only axial movement on the shaft. All these motors have the disadvantage of a substantial increase of the machine length, as well as unsafe operation due to the possibilities of blocking the brake deblocking armature at its joint with the shaft.